The soybean cyst nematode (SCN), Heterodera glycines, is the primary biotic factor limiting soybean production in the United States, accounting for 40% of total disease losses (Wrather, J. A., Anderson, T. R., Arsyad, D. M., Gai, J., Ploper, L. D., Porta-Puglia, A., Ram, H. H., Yorinori, J. T. 1997. Soybean disease loss estimates for the top 10 soybean producing countries in 1994. Plant Disease 81:107-110). The nematode is a relatively recent introduction to Kansas (Sim, T., I V., and Todd, T. C. 1986. First field observation of the soybean cyst nematode in Kansas. Plant Disease 70:603), yet it's present distribution encompasses 40 counties across six of the nine state districts. Based on the results of an extensive grower sampling program (SCN Coalition), approximately 10% of the state's soybean production fields are estimated to be infested with H. glycines, with nematode prevalence in several areas exceeding 40%. Yield losses in individual infested fields in Kansas range from 10% to 40%, depending on environment (Todd, T. C., Schapaugh, W. T., Long, J. H., and Holmes, B. 1995. Field response of soybean in maturity groups III-V to Heterodera glycines in Kansas. Supplement to the Journal of Nematology 27:628-633.).
Nonhost crops and resistant varieties are the most widely used management strategies for SCN. Both effectively reduce nematode population densities, but declines in the North Central region are relatively slow and elimination unlikely. Resistance, while readily available for the most common variants (races) of SCN, has a narrow genetic base (˜85% of resistant varieties derive their resistance from a single source), and is limited or unavailable for some populations. In addition, adaptation of nematode populations to resistant varieties poses a significant threat to the long-term management of this pest (Holmes, B. A., Todd, T. C., and Schapaugh, W. T. 1999. Effect of resistance source on SCN populations. National Soybean Cyst Nematode Conference, Orlando, Fla., Jan. 7-8, 1999; Young, L. D. 1998. Managing soybean resistance to Heterodera glycines. Supplement to the Journal of Nematology 30:525-529).
Novel approaches to SCN management are needed to complement current strategies, and prolong the effectiveness of available resistance genes.